The news just seems to be getting worse and worse coming out of the Arctic and Antarctic. The melting of ice is not appearing to let up, and is in fact, getting faster. A new NASA-funded satellite study shows that the two biggest ice sheets on Earth — Greenland and Antarctica — are losing mass at an accelerating rate. This is the longest study ever conducted to analyze changing ice conditions at the poles, spanning nearly 20 years. Researchers concluded that the melting of ice caps has overtaken the melting of mountain glaciers to be the most dominant source of global sea level rise, much sooner than previous forecast models predicted.

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Over the length of the study, the ice caps have lost an average combined mass of 475 gigatons per year (1 gigaton = 1 billion metric tons). Over the course of the study, that number has risen by 36.3 gigatons for each consecutive year on average. In comparison, the loss of mountain glaciers was estimated at 402 gigatons per year on average. However, the rate of acceleration for mountain glacier loss is three times smaller than that of the ice caps.

"That ice sheets will dominate future sea level rise is not surprising -- they hold a lot more ice mass than mountain glaciers," said lead author Eric Rignot, jointly of NASA's Jet Propulsion Laboratory, Pasadena, Calif., and the University of California, Irvine. "What is surprising is this increased contribution by the ice sheets is already happening. If present trends continue, sea level is likely to be significantly higher than levels projected by the United Nations Intergovernmental Panel on Climate Change in 2007. Our study helps reduce uncertainties in near-term projections of sea level rise."

Over the next four decades, the researchers conclude that if ice sheets keep melting at their current rate, sea levels could rise by 15 centimeters (5.9 inches) by 2050. However, they caution that there are number of uncertainties remaining in accurately predicting future ice loss acceleration.